1. Field of the Invention
The present invention relates to, and the field of the invention is, sacrificial metal anodes utilized in the tank of an electric water heater having a metal shell to protect the shell from corrosion, i.e., the depletion of metal, due to the action of galvanic currents flowing in the water in the tank. This field of sacrificial metal anodes is presently classified in class 204 subclass 196 and class 219 subclasses 318, 322 and related classes.
More specifically, the present invention relates to an easily replaceable, flexible, elongate sacrificial anode attachment which is insertable into a water tank through an opening provided in the shell of the tank for mounting an electric immersion heater in the tank and which is electrically, mechanically and detachably connected to the legs of the heater situated in the tank.
2. Description of the Prior Art
It has been known for some time that galvanic currents in partially ionized water in the tank of an electric water heater cause corrosion of (depletion of metal from) the metal shell of the tank.
To combat this corrosion the inner surface of the metal shell is often coated with ceramic, glass, metal or other protective material. However, the coating is or may become faulty and it is difficult, if not impossible, to cover all exposed areas of the inner surface of the metal shell. Addditionally the galvanic currents often cause corrosion of the sheath surrounding the heating elements immersed in the tank. Consequently, in addition to coating the inner surface of the tank, it is customary to mount a sacrificial metal anode in the tank. The anode is made of a metal, typically magnesium, which is anodic to the metal shell, typically made of steel. With this arrangement, the galvanic currents will act upon the deplete metal from the sacrificial metal anode (which is made of a metal higher in the electromotive series than is the metal of which the shell is made) thereby to prevent depletion (corrosion) of metal from the metal shell.
Typically, the sacrificial metal anode is an elongate, magnesium rod which is secured to and depends from the top inner surface of the tank. Often the anode is mounted near the center-line of the tank and supported from a combination fitting received in a threaded opening in the top of the tank, the fitting and threaded opening serving also as an outlet for the hot water connection to the tank. In this arrangement, the anode is usually soldered into and forms a solid part of the plumbing system. As such the anode is accessible only after removing the top outer jacket of the water heater. This can be accomplished only after disconnecting the hot and cold water pipes and frequently after disconnecting the electric power as well.
Also, because of limited "head room" above an installed water heater, it is almost impossible to insert a replacement, elongate, magnesium anode rod into the top threaded opening. Replacement could, of course, be accomplished by fully disconnecting the water heater and tipping it over onto its side.
From the forgoing remarks, it is apparent that replacement of a conventional elongate sacrificial anode entails considerable labor and is time consuming and cumbersome.
Such replacement is often desirable, however, due to the depletion of the metal anode, typically 4 or 5 years after the installation of the tank.
To permit a simplified replacement of the sacrificial anode, it has heretofore been proposed to form the anode as a closed tube, sheath or cover which is suitably joined or attached to the heater unit. More specifically, the anode is fitted over or about the sheathed hairpin shaped heating element of the electric immersion heater and forms a part thereof which is inserted into the tank through the opening provided therefor. In this way, both the heating element and sacrificial anode are simply mounted in the tank and are easily replaced. An example of such an anode can be found in U.S. Pat. No. 3,176,115 issued to E. W. Balis on March 30, 1965.
The sacrificial anode attachment of the present invention differs from the combination heating element and anode disclosed in the patent referred to above, by providing an elongate, flexible anode which does not isolate the heating element sheath from direct contact with the water, which provides considerably more anode material and more anode surface area in contact with the water, and which correctly locates the anode near the central vertical axis of the tank to yield nearly uniform galvanic current flow to all interior surface areas of the tank.